The present invention relates to a process and an apparatus for producing a bag film web for use in the production of reclosable plastic bags, and more particularly, to a method and process for applying a zipper containing a profile with adjacent ribs to a traveling film web.
Reclosable plastic bags have been used in a wide variety of applications. Reclosable plastic bags are typically formed, sealed and cut to form a container having three closed sides, and one reclosable side. The reclosable side of the bag includes a male fastener element and a female fastener element which are placed in an opposed relation. The user can engage the male and female fastener elements to seal the bag, and can disengage the male and female elements to gain access to the interior of the bag.
A male fastener element typically consists of a male closure profile having a head which is shaped to be received by a cavity of a female closure profile. For example, Ausnit, U.S. Pat. No. 3,338,284 disloses a fastener element having an arrow-shaped head which is sized and shaped to be received by a mushroom-shaped cavity in a generally C-shaped female closure profile. Although closure elements of the type shown in the Ausnit patent can be manufactured to function quite well, room for improvement exists.
One improvement relates to the use of a fastener element wherein the male profile element is joined by a pair of adjacent ribs. This type of fastener element consists generally of a standard female closure profile which is used in conjunction with a modified male closure profile. The male closure profile is modified to include a first rib member which is disposed on one side of the closure profile, and a second rib member which is disposed on the other side of the closure profile. Both the first and second rib members extend in a generally parallel, spaced relation to the male closure profile. The rib members improve the operation of the zipper by stiffening the area of the bag film around the male closure profile member, thereby helping the user to align and engage the male and female closure profile members. Additionally, it is believed that the rib members better distribute the closing force exerted by the user over a greater area of the bag film, thus making the user feel as though the male and female closure members are easier to engage.
Conventionally, this type of zipper is formed by extruding the male closure profile and rib members integrally with the extrusion of the bag film web. Although this integral extrusion process can function quite well in forming a fastener having rib adjacent to the profile member, it has some drawbacks. The primary drawback of the integral extrusion process is that it limits the manufacturer's flexibility in the production of reclosable bag film webs. As the integral extrusion process requires that the bag film and closure member be formed at the same time, the manufacturer cannot use the integral extrusion process to place a closure member onto an existing bag film web. The flexibility to place a closure member onto an existing bag film web is often desirable in prototype applications, low volume applications, specialty applications, and applications wherein the purchaser desires to purchase his bag film material from one source, and his closure members from a second source.
To overcome this lack of flexibility, it would be helpful to be able to form the closure member separately from the formation of the bag film web, and to join the closure member to the bag film web thereafter.
One method of applying a rib containing closure member to a preformed bag film web is to extrude a base member, a closure profile, a first rib member and a second rib member together as a unitary extrudate. The underside surface of the base portion of the resulting unitary extrudate is then joined to a traveling bag film web. Although this method has been utilized successfully in some applications, in other applications air has become entrapped between the rather wide base and the underlying film web. This can result in poor adherence of the closure member to the web and less than satisfactory operation of the zipper in use.
Accordingly, it is an object of the present invention to provide a method for forming the closure profile and rib members of a zipper as separate extrudates and then joining them to a traveling bag film web.